Multidrug resistant Staphylococcus aureus (e.g., methicillin resistant [MRSA]) and enterococci (e.g., vancomycin resistant [VRE]) emerged in the 1960's and 1980's, and are leading causes of life-threatening infection in the hospital - more recently also in the community. Critically, after 20 years of containment, vancomycin resistance moved from VRE to MRSA, creating VRSA, and there are now 10 well documented cases. The overall goal of this program project is to identify and develop new drugs for treating infections caused by VRSA and VRE. This will be conducted hand-in-hand with studies to understand the development and proliferation of resistance in the multidrug resistant microbes being targeted in this Subproject. Overarching Goals: Determine what genetic or biological events led to the breach of containment of vancomycin resistance in VRE and transfer to VRSA, and demonstrate the activity of new compounds against them, by discovering and examining: -a known genetic event (insertional inactivation of a plasmid borne postsegregational killing TA module), - unknown traits within the genomes of the 10 well documented VRSA strains, and the putative VRE donors coisolated with them, - genetic and metabolic compatibilities, that may have predisposed them to coexist in mixed infection or participate in vancomycin resistance transfer, and - the efficacy of compounds developed in this PPG against these highly multidrug resistant, hospital adapted strains By understanding the basis for transfer as well as the nature of these increasingly resistant strains, we will be better positioned to assess the threat of continued erosion of antibiotic sensitivity in leading causes of hospital and community infection in the US, and will be alert to the types of conditions that promote this transfer.